Now, it doesn't really matter when you start to learn magic, I just know that it is a very useful resource to have. First thing you need to do is obtain 1500gp and travel to Varrok, in Varrok go the the central square and look for the staff shop. In there buy an air staff.
Casting The First Spell
Now either: Runecraft (lvl 3) or buy as many mind runes as
you can, now go to the combat interface and select spell with
the sheild (That will put up your defence as well) and select the
wind attack. Now travel to the lumbridge bride and start attacking
goblins, you will fire up to level 7/8/9 in no time. And now you
can cast new spells.
Advancing Up The Levels
Now you can cast new spells, so simply buy or rune craft the
runes that you need and you will shoot up the ranks in magic.
Here are some tricks that I learned and will help.
In Varrok when you enter via East entrance, there are some
level 21 guards posted. There are also some rocks near there, get
behind the rocks and face the guards and attack, they will get trapped
and you can keep smashing them until they die.
In the dwarven mines, if you enter via the entrance in Falador
(Go east of the furnace and it is next to the east wall), there are
some level 13 scorpions. stand inside the copper area and the
scorpions can't get you. So you can kill them... or mine.
Don't Do These Things
Don't beg for runes/money, it is the most annoying thing ever.
Stop attacking an enemy just because you aren't doing damage
Just because the enemies name is green, dosnt mean you can
kill them, with magic. The name is compared to your combat level so
for example if your combat level was 20 and your magic level was 7
don't go killing level 13 skeletons you will die.
Thanks for reading.